1. Field of the Invention
This invention relates to an injection compression molding method and a temperature control apparatus for performing the same method.
2. Description of the Prior Art
The conventional injection compression molding method, which uses either improved metallic molds for injection molding or improved metallic molds for compression molding, is performed in such a manner that the metallic molds are previously warmed and synthetic resin is injected therein. Then gate portion is mechanically sealed or the smaller thickness portion at the gate is cooled and solidified to be sealed so that synthetic resin filled in the cavity is restrained from counterflowing from the gate, thereby performing the compression. The metallic molds are opened after cooling and setting the synthetic resin within the cavity so that the molded product may be taken out. In addition, the temperature control of metallic molds in the molding cycle is performed by keeping a constant temperature throughout one molding cycle, or by heating the metallic molds just before injection and rapidly cooling them after injection compression.
The conventional injection molding method, when intended to mold the article larger in thickness or nonuniform in thickness, easily leaves sink marks or a residual stress-strain. In spite of that, the molded product conventionally is thrown into water to be cooled for shortening the molding cycle. Conventionally, in order to restrict the sink marks from being created when the temperature of synthetic resin is high, it is necessary to apply a high pressure to the synthetic resin by means of an injection pressure or a high compression pressure by the injection compression molding apparatus. In order to accomplish this result, an injection cylinder must be given a ultra-high pressure, or the high compression pressure molding must be performed. For example, the catalogue of the injection molding machine called Coining Machine (Sandwich Press in synonym) manufactured by ENGEL CORPORATION in Australia, describes that it is preferable to inject synthetic resin under a pressure of 300 to 400 kg/cm.sup.2 and to apply to it a compression pressure of 700 to 800 kg/cm.sup.2. In usual compression molding, however, the compression pressure of 100 to 800 kg/cm.sup.2 is applied perpendicularly, which differs considerably from the compression pressure for the aforesaid injection compression molding machine. Hence, the injection compression molding machine will require a remarkably excessive mold clamping force in comparison with the compression molding machine.